The construction and mode of operation of hydrocyclones are well known in the industry. Initially, offshore platforms used to employ large separating vessels to treat separation water. The high cost to accommodate such systems encouraged the development of de-oiler hydrocyclones for the offshore oil industry in the 1980's, rapidly making them standard equipment for recovery of oil from production waters.
Hydrocyclones are equipment that separate liquid and/or particulate in mixtures or in suspension which may be based on the density of the liquids or the density of the particles, respectively. The hydrocyclone is usually comprised of a cylindrical section at the top comprising a tangential liquid inlet aperture and a conical base. The angle and the size of the conical section play an important role in the performance of the equipment. The module usually has two outputs in opposite positions: the overflow or tailing, whereby the less dense liquid is ejected and the underflow through which the higher density liquid is ejected under higher flow.
Internally, a centrifugal force produces a rapid acceleration of the fluids, causing the denser liquid to flow towards the walls and then through the underflow, and the less dense liquid to flow towards the outlet referred to as tailing. The diameter of the tailing outlet is 1.5 to 5 mm in diameter when the separator is of liquid/liquid type. One disadvantage of this type of system is that often, materials such as asphaltenes deposit and build up within the hydrocyclones, decreasing performance and often causing equipment clogging.
Hydrocyclones may be composed of hydrocyclone liners arranged within a vessel. In general, they are arranged in packages of dozens of liners (56, 72, . . . ), with the inlets and outlets common to liners, in communication with the underflow and overflow. Several systems involve a large number of liners employed in a complex pipe inlet and outlet system that communicate with a separation system plant, which takes up a lot of space and requires a high-cost support structure.
U.S. Pat. No. 6,918,494 shows an improvement in the arrangement of liner packages within the separator vessel to reduce space and allow accommodation of a greater number of liners. Such upgrading is of extreme importance for applications on offshore platforms and FPSOs where space is an important issue. The reduction of space occupied by a compact arrangement minimizes equipment costs and improves the flow of distribution to the liner inlets.
Currently, lighter crude oil resources are declining, leaving an increasing share of supply of increasingly heavier oils. Sources of heavy oil are still plentiful, with no more than 3% of the heavy oil discovered being currently produced. As a result, heavy oils are expected to play an increasingly important role in oil production.
Production separators are one of the most disturbed equipment due to instabilities in the flow of fluids from oil producing wells. The separators, besides promoting phase separation (water, oil and water), dampen production oscillations. On the other hand, load and space restrictions in offshore units require the equipment to be compact, which makes them more sensitive to the production oscillations.
Among the usual separation equipment, we have the hydrocyclones, designed to separate sand from the inlet fluid (de-sanders), de-waters, and/or de-oilers. Currently, in order to bypass the problems of fields that produce a lot of water and prevent this water from being treated on the platforms or topsides (FPSOs), subsea separation systems have been developed. However, such equipment requires maintenance and is installed in hostile and difficult to reach environments. This type of equipment suffers even more under the conditions of operation with heavy oils, which can lead to clogging of this equipment.
The purpose of this invention is to develop an oil/water separation system which alleviates problems related to maintenance and space in subsea equipment and which consists of desander, hydrocyclone and/or de-water modules. Thus, it will provide a novel and improved option for the treatment of mixtures, especially mixtures from the oil production process, such as heavy oils.
In view of the increased use of heavy oils in the oil producing industry, the present invention provides a recoverable subsea module which provides ease of intervention and/or equipment replacement. Such module may be applied to mix separation systems and may be extended to any apparatus which comprises a vessel containing hydrocyclones or liners grouped therein to carry out a process.